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The Western Cordillera (also called North American Cordillera, Western Cordillera of North America, Pacific Cordillera and, in Canada in reference to the Canadian portion, the Canadian Cordillera) covers an extensive area of mountain ranges, basins, and plateaus in western North America. The area covers much of western North America west of the Western Great Plainsmarker. Mountain ranges, plateaus, contiguous intermontane basins, and plateaus are included in the geographical context and in reference to the Western Cordillera. Western Cordillera or Pacific Cordillera is oftentimes used to define or refer to areas within the Western Cordillera. (i.e. the Pacific Coast Ranges).

The Western Cordillera extends from the U.S. state of Alaskamarker and south to Mexicomarker. Mountains ranges generally run longitudinally along three main belts, including the Coast Range belt, along the Pacific Margin, the central Nevadan Belt, and the inland Laramide belt. The northern extent begins in the Western Brooks Range, De Long Mountains, and Lisburne Hills of Northern Alaska.. The area extends south through the diverse topography of the Yukon Territory and British Columbia - the Saint Elias Mountainsmarker and Coast Mountainsmarker along the Pacific coast. In the Yukon the Yukon Ranges and Yukon Plateaumarker lie to the northeast of the Saint Elias Mountains and to the north and east of the Coast Mountains, beyond which the Eastern System of the Cordillera comprises the Selwyn Mountainsmarker, forming the spine of the border between the Yukon and the Northwest Territoriesmarker, and the Mackenzie Mountainsmarker. In British Columbia, inland from the Coast Mountains lie the Interior Mountains, Interior Plateaumarker and Columbia Mountains, comprising what is known in Canada as the Interior System, to the Rocky Mountains, which form the southern half of the boundary between British Columbia and Alberta and are the British Columbia component of the Eastern System (some categorizations describe the Selwyns and Mackenzies as an extension of the Rockies, but this is not part of the official toponymy).

In the United States major features of the region include the Cascade Ranges, Central Oregon Highlands, the Colorado Plateau, and the Sierra Nevada in California. The southern extent of the Western Cordillera ends in the Sierra Madre Occidental and Sierra Madre del Sur of Mexico.

Geologic origin

The historical geomorphology and orogenic development of the Western Cordillera (North America) is dynamic and controversial, but the paleoenvironmental details provide context on the geography (physical geography, human geography, and biogeography) and how it evolved to its modern state. For example, the Laramide orogeny changed the topography of the central Rocky Mountains and adjoining Laramide regions (from central Montana to central New Mexico) during the Late Cretaceous 80 million years ago. Prior to this time the Rocky Mountain region was occupied by a broad foreland basin. Topographic relief continued to evolve with much activity occurring in the middle Eocene (50-55 million years ago), but since this time the deformation of the region has been relatively stable. High altitude formations were common during the Eocene and Oligocene. Orogenic activity is recorded in the Pacific Coastal Mountains (Cascade and Sierra) during the Oligocene, but major uplift did not occur in this area until after the Miocene. The coastal and interior mountains were higher during the Eocene than at present.

Pacific Coast Ranges

The Pacific Coast Ranges from southeastern Alaska and southern Yukon paralleling the coast 150 or 200 miles inland and are comprised of several mountain systems, from north to south the Saint Elias Mountainsmarker, Coast Mountainsmarker, the Cascade Range (officially the Cascade Mountains in Canada), the Insular Mountains, the Olympic Mountainsmarker, the Oregon and California Coast Ranges, and the Sierra Nevada.

Saint Elias Mountains

Coast Mountains

The Coast Mountains run from the lower Fraser River and the Fraser Canyonmarker northwestward, separating the Interior Plateaumarker from the Pacific Ocean. Their coastal flank is characterized by an intense network of fjords and associated islands, very similar to the Norwegian coastlinamarker, while their inland side against the plateau they transition to the high plateau in dryland valleys notable for a series of large lakes similar to the alpine lakes of southern Switzerland, beginning in deep mountains and ending in flatland. They are subdivided in three main groupings, the Pacific Ranges between the Fraser and Bella Coolamarker, the Kitimat Rangesmarker from there northwards to the Nass River and the Boundary Ranges from there to their terminus in the Yukonmarker Territory at Champagne Passmarker and Chilkat Passmarker northwest of Haines, Alaskamarker. The Saint Elias Mountainsmarker lie to their west and northwest, while the Yukon Ranges and Yukon Basin lie to their north. On the inland side of the Boundary Ranges are the Tahltanmarker and Tagish Highlands and also the Skeena Mountains, part of the Interior Mountains system, which also extend southwards on the inland side of the Kitimat Rangesmarker.

The terrain of the main spine of the Coast Mountains is typified by heavy glaciation, including several very large icefields of varying elevation. Of the three subdivisions, the Pacific Ranges are the highest and are crowned by Mount Waddingtonmarker, while the Boundary Ranges contain the largest icefields, the Juneau Icefieldmarker being the largest. The Kitimat Ranges are lower and less glacier-covered than either of the other two groupings, but are extremely rugged and dense.

The Coast Mountains are made of igneous and metamorphic rock from an episode of arc volcanism related to subduction of the Kula and Farallon Plates during the Laramide orogeny about 100 million years ago. The widespread granite forming the Coast Mountains formed when magma intruded and cooled at depth beneath volcanoes of the Coast Range Arc whereas the metamorphic rock formed when intruding magma heated the surrounding rock to produce schist.

Insular Mountains

The Insular Mountains extend from Vancouver Islandmarker in the south to the Queen Charlotte Islandsmarker in the north on the British Columbia Coast. It contains two main mountain ranges, the Vancouver Island Rangesmarker on Vancouver Island and the Queen Charlotte Mountains on the Queen Charlotte Islands.

Olympic Mountains

Cascade Range

The Cascade Range extends from Northern California, United States to southern British Columbiamarker, Canada. It consists of non-volcanic and volcanic mountains : all of the known historic eruptions in the contiguous United States have been from the volcanoes of the Cascade Volcanic Arc, which is a different entity and extends into the southern Coast Mountainsmarker. The highest peak in the Cascade Range is Mount Rainiermarker ( , a volcano. The small portion of the Cascade Range in Canada is called the Cascade Mountains or Canadian Cascades and in its southwestern area is similar in terrain to the area north of Glacier Peakmarker known as the North Cascades and its northern and eastern extremities verges into the Thompson Plateaumarker in less rugged fashion than most other parts of the range. The North Cascades is very different in character than the series of high volcanic cones from Rainier southwards to Mounts Shastamarker and Lassenmarker and is more severely alpine and steeply rugged, in particular the Hozomeen Rangemarker. Inland portions of the range are dryland and plateau-like in character, e.g. the Okanagan Rangemarker, which lies along the Cascades' northern limit along the Similkameen Rivermarker.

Oregon Coast Range

The Oregon Coast Range is the part of the Coast Range system that is denoted as between the mouth of the Columbia River and the Middle Fork Coquille River. It is about long, placing the eastern part of Oregon in a rain shadow. The highest peak is Marys Peakmarker, at 4,101 ft/1,249m.

California Coast Ranges

Sierra Nevada

The Sierra Nevada form an inland mountain spine of California running south from the area of the terminus of the Cascade Range near Mount Lassenmarker along the east flank of the Central Valley of Californiamarker to the Mojave Desert, forming a mountain region of complex terrain and varied geology which separates the Central Valley from the Great Basin which lies inland to the east. The height of the mountains in the Sierra Nevada gradually increases from north to south, culminating at Mount Whitneymarker ( ), the highest point in the Continental United States. From east to west, the Sierra are shaped like a trapdoor: the west slope gradually rises, and the east slope forms a steep escarpment.

The northern Sierra are predominately volcanic rock, while the southern Sierra are granite (formed deep underground in the Jurassic period), and then subsequently sculpted by glaciers into dramatic U-shaped valleys and aretes.

Brooks Range

The Brooks Range


The Brooks Range are the northernmost of the major mountain systems of the Western Cordillera, and extend along an east-west axis across northern Alaskamarker from near the northern opening of the Bering Straitmarker to the northern Yukonmarker Territory. Major subranges include the British Mountains and Richardson Mountainsmarker, towards their eastern end, and at their farthest west is the small subrange that De Long Mountainsmarker. The Brooks Range forms the northern flank of the lower Yukon Rivermarker basin, separating it from Alaska's North Slope region, facing the beaufort Seamarker.

Rocky Mountains and Trench

The Rocky Mountains stretch more than from northernmost British Columbiamarker, in Canada, to New Mexicomarker, in the United States. The range's highest peak is Mount Elbertmarker in Coloradomarker at above sea level. The Rockies rise steeply over the Interior Plains to the east, and over the Great Basin to the west (in the United States), and over the Rocky Mountain Trenchmarker (in Canada).

Columbia Mountains

Location map


The Columbia Mountains are a designation in British Columbia for a group of four ranges lying between the Rocky Mountain Trenchmarker and the Interior Plateaumarker. These are the Cariboo Mountainsmarker, which are the northernmost and sometimes considered to be part of the Interior Plateau, the Selkirk Mountainsmarker, the Purcell Mountains, and the Monashee Mountains. The Selkirks and Purcells lie entirely within the basin of the Columbia River, while the Monashees lie to the river's west on its southward course from its Big Bend and are flanked on the west by the basin of the Thompson and Okanagan Rivers. There are many named subranges of all four subgroupings, particularly in the Selkirks and Monashees. The southward extension of the Selkirks, Purcells and Monashees into the United States are reckoned to be part of the Rocky Mountains and the designation Columbia Mountains is not used there (the Purcells, also, go by the name "Percell Mountains" in the United States). The Salishmarker and Cabinet Mountains south of the Kootenai River are essentially part of the same landform, but are officially designated part of the Rocky Mountains in the United States.

Monashee Mountains
To the west of the Monashees and Cariboos, there are three intermediary upland areas which are transitional between the mountain ranges and the plateaus flanking the Fraser and Thompson Rivers. These - the Quesnel, Shuswapmarker and Okanagan Highlandsmarker, are sometimes considered as being part of the neighbouring ranges rather than the plateaus and are often spoken of that way locally but are formally designated as being part of the Interior Plateaumarker. The southernmost extends into the Washington, where it is named by the American spelling Okanogan Highland (and was the first-named of these groupings).

Interior System

Colorado Plateau



The Colorado Plateau is an area of high desert located in Arizonamarker, New Mexicomarker, Coloradomarker, and Utahmarker, bisected by the Colorado Rivermarker which flows westward through the southern part, and the Green River which flows south from the northernmost part of the plateau. The Green is a tributary of the Colorado, the confluence being west of Moab, Utah in Canyonlands National Park.

Great Basin



The Great Basin covers most of the state of Nevadamarker and parts of the states of Californiamarker, Arizonamarker, and Utahmarker, bordered by the Sierra Nevada to the west and the Wasatch Mountains to the east. It is an extremely arid and flat region covering over 400,000 square miles (1,035,995 square kilometers).

Interior Plateau



The Interior Plateau is the northern continuation of the Columbia Plateaumarker, covering much of inland British Columbiamarker. The Cariboo Mountainsmarker and Monashee Mountains lie to the east, the Canadian Cascades are to the southwest, and the Hazelton Mountainsmarker and Coast Range to the west and northwest.

Thompson Plateau



The Thompson Plateau forms the southern portion of the Interior Plateau. It is bordered on the south by the Canadian Cascades and on the north by the Thompson River.

Okanagan Highland



The Okanagan Highland is to the east of the Thompson Plateau, and is bounded by the Okanagan River on the west, the Shuswap Rivermarker on the north, and the Kettle River on the east side. The Okanagan Highland is described as being a hilly plateau, and is located in southern British Columbiamarker and northern Washingtonmarker.

Shuswap Highland



The Shuswap Highland consists of a portion of the foothills between the Thompson Plateaumarker and Bonaparte Plateaumarker on the west, and the Monashee Mountains and Cariboo Mountainsmarker on the east and northeast.

Quesnel Highland

Fraser Plateau

Nechako Plateau

McGregor Plateau

Interior Mountains

Hazelton Mountains

Cassiar Mountains

Stikine Ranges

Omineca Mountains

Skeena Mountains

The Skeena Mountains run along the upper reaches of the Skeena River in British Columbia.

Yukon Ranges

Mexican Cordillera

Sierra Madre Occidental

Sierra Madre del Sur

See also



References

  1. R. Saager and F. Bianconi. (1971). The Mount Nansen gold-silver deposit, Yukon territory, Canada. Mineralium Deposita, 6(3): 209-224
  2. D. S. Cowan. (1985). Structural styles in Mesozoic and Cenozoic melanges in the Western Cordillera of North America. Geological Society of America Bulletin 96, no. 4: 451-462
  3. A. J. Eardley. (1967). Western Cordillera--Alaska to Mexico: ABSTRACT. AAPG Bulletin, Volume 51.
  4. T. O. Tobisch, S. R. Paterson, S. Longiaru, T. Bhattacharyya. (1987). Extent of the Nevadan orogeny, central Sierra Nevada, California. Geology, 15(2):132
  5. P. J. Coney and T. A. Harms. (1984). Cordilleran metamorphic core complexes: Cenozoic extensional relics of Mesozoic compression. Geology, 12:550-554. [1]
  6. A. J. Martin. (1970). Structure and Tectonic History of the Western Brooks Range, De Long Mountains and Lisburne Hills, Northern Alaska. Geological Society of America Bulletin 81, no. 12: 3605-3622.
  7. E. C. Cano, D. J. M. Zenteno, J. U. Fucugauchi. (1986). Paleomagnetismo Y terrenos tectonoestratigraficos de Mexico. 89-102. [2]
  8. M. E. McMillan, P. L. Heller, and S. L. Wing. (2006). History and causes of post-Laramide relief in the Rocky Mountain orogenic plateau. Geological Society of America Bulletin 118, no. 3-4: 393-405.
  9. W. R. Dickinson, M. A. Klute, M. J. Hayes, S. U. Janecke, E. R. Lundin, M. A. McKittrick, and M. D. Olivares. (1988). Paleogeographic and paleotectonic setting of Laramide sedimentary basins in the central Rocky Mountain region: Geological Society of America Bulletin, v. 100 p. 1023-1039
  10. J. A. Wolfe, C. E. Forest, and P. Molnar. (1998). Paleobotanical evidence of Eocene and Oligocene paleoaltitudes in midlatitude western North America. GSA Bulletin, 110(5): 664-678
  11. D. Alt and D. Hyndman. (1995). Northwest Exposures: A Geological Story of the North West. Mountain Press Publishing Company, Missoula, Montana
  12. Brunsfeld, S., Sullivan, J., Soltis, D., Sotis, P., 2001. Comparative phylogeography of north-western north america: A synthesis. In: Silverton, J., Antonovics, J. (Eds.), Integrating Ecology and Evolution in a Spatial Context. The 14th Special Symposium of the British Ecological Society. British Ecolological Society, Blackwell Science Ltd., Ch. 15, pp. 319–339.[3]
  13. S. Holland, Landforms of British Columbia, BC Govt, 1976
  14. Colorado Plateau in the GNIS (Geographic Names Information System)
  15. Great The in the GNIS (Geographic Names Information System)
  16. Interior Plateau in the BCGNIS (British Columbia Geographic Names Information System)
  17. Thompson Plateau in the BCGNIS (British Columbia Geographic Names Information System)
  18. Okanagan Highland in the BCGNIS (British Columbia Geographic Names Information System)
  19. Shuswap Highland in the BCGNIS (British Columbia Geographic Names Information System)



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